The disclosure of Japanese Patent Application 11-362578 filed on Dec. 21, 1999, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an improvement in a valve for controlling reciprocating flow of a fluid and, more particularly, to a flow control valve effectively employed as a switching valve that discharges air in response to a rise in the internal pressure of a tank or during a refueling process and introduces fresh air in response to a fall in the internal pressure of the tank or during a purging process.
2. Description of Related Art
FIG. 5 is a system diagram of a breathing mechanism of a fuel tank for motor vehicles.
A fuel tank 1 is installed in a motor vehicle and provided with a breathing mechanism. When the internal pressure of the fuel tank 1 is high, the breathing mechanism operates such that fuel vapors in the fuel tank 1 are adsorbed by a canister 3 through a breather line 2 and escape to the outside through a vent line 4.
If the pressure in the fuel tank 1 falls, the breathing mechanism introduces outside air into the fuel tank 1 through the vent line 4 and the canister 3.
The vent line 4 is provided with a flow control valve 6 and a filter 7. The flow control valve 6 is designed as a diaphragm-type switching valve that opens in response to a rise in the pressure of the fuel tank 1 to discharge air to the outside and introduces outside air into the fuel tank 1 in response to a fall in the pressure of the fuel tank 1. The filter 7 removes dust from outside air and thus prevents the canister 3 and the valve from being stained.
FIG. 6 shows the cross-sectional structure of a flow control valve according to the related art.
The flow control valve 6 has a diaphragm-type valve body 11 and a valve port 12 opened and closed by the valve body 11. In addition, the flow control valve 6 has a communication port 13 leading to the side of outside air 8 and a communication port 14 leading to the side of the canister 3. The valve port 12 is formed at the end of the communication port 13 leading to the side of outside air 8. If the valve port 12 is opened, the communication port 13 and the communication port 14 thereby come into communication with each other. A check valve 15 is disposed between a communication port 20 leading to the side of the filter 7 and the communication port 14 leading to the side of the canister 3. The check valve 15 allows flow in a direction from the communication port 20 to the communication port 14 and prohibits flow in a direction from the communication 14 to the communication port 20.
A back pressure chamber 16 of the diaphragm-type valve body 11 communicates with outside air through a pipe portion 17 and a hose 18 and is capable of sucking and discharging air. The hose 18 extends downwards to prevent water from entering the back pressure chamber 16. In order to prevent dust from entering the back pressure chamber 16, the pipe portion 17 is provided with a dust filter 19.
In the flow control valve 6 shown in FIG. 6, the valve body 11 opens the valve port 12 in response to a rise in the pressure of the fuel tank 1.
Then fuel vapors in the fuel tank 1 enter the communication port 13 through the canister 3 and the communication port 14, so that it becomes possible to discharge air.
If the pressure in the fuel tank 1 falls, outside air reaches the communication port 14 through the air filter 7, the communication port 20 and the check valve 15, and is introduced into the fuel tank 1 through the canister 3.
In this manner, it becomes possible to suck and discharge air in response to a change in the internal pressure of the tank and introduce outside air when purging the canister.
Furthermore, the back pressure chamber 16 of the diaphragm-type valve body 11 operates smoothly only on condition that air be sucked and discharged in accordance with vertical movements of the valve body 11. Because outside air is introduced into the back pressure chamber 16 through the hose 18, the pipe portion 17 and the dust filter 19, no trouble is caused to the operation of the valve body 11.
However, since the flow control valve shown in FIG. 6 achieves introduction of air into the back pressure chamber 16 and prevention of water exposure by providing the hose 18 and the dust filter 19, the number of parts increases and the costs soar. Also, the height of the flow control valve increases, so that restrictions are imposed on installation space.
The structure wherein the air filter 7 is disposed separately from the flow control valve 6 also imposes some restrictions on installation space.
It is an object of the invention to provide a compact and light-weight flow control valve that imposes no restrictions on installation space and can be manufactured at low costs.
In order to achieve this object, one aspect of the invention is a flow control valve includes a diaphragm-type valve body, a valve port opened and closed by the valve body and a first port. The flow control valve also includes a second port coming into communication with the first port when the valve body is opened. A back pressure chamber of the valve body communicates with the first port through a vent hole formed in a case of the flow control valve.
According to the aforementioned aspect, since the air filter is integrated with the flow control valve, no restrictions are imposed on installation space.
Moreover, the reduced number of parts contributes to the reduction of costs.
The back pressure chamber of the valve body communicates with out side air through a vent hole formed in a case of the flow control valve.